1. Field of the Invention
The present invention relates to a hot press for producing a multilayered substrate such as a multilayered ceramic substrate, in particular, to a hot press suitable for forming a high performance and high surface pressure ceramic substrate and the like.
2. Description of the Related Art
Due to an increase in the density and the number of layers of a multilayered ceramic substrate formed by a hot press, a higher performance hot press has been required for producing such a multilayered ceramic substrate, which can handle the variations in outside dimensions of the multilayered ceramic blanks and which reduces superposition errors between one layer and another layer.
One conventional technique to achieve the requirements described above is disclosed in Japanese Patent Application Laid-Open No. 59-114894, in which a substrate blank is vacuum-packed and then forming is effected by heat and hydrostatic pressure.
However, processing under hydrostatic pressure results in poor productivity. To avoid this problem, there is a technique in which a frame fixture of high rigidity metal is provided on a heating plate of a hot press wherein the frame fixture has dimensions larger than the outside dimensions of substrate blanks to be formed by several ten microns, and substrate blanks are put in the metal frame fixture so as to perform forming by pressing and heating them between the fixture and an upper heat plate.
When blanks are pressed in the vertical direction to form a multilayered substrate, because only atmospheric pressure is applied to a periphery of the blanks, some of blanks at the periphery are put out due to the difference in pressure between the outside and the inside. As a result, the density is lower at a peripheral region than at a central portion of the substrate.
In the above-mentioned conventional technique using a metal frame fixture, a rather large space is required between the fixture and substrate blanks to improve productivity. Thus, it is impossible to prevent the substrate blanks from being put out.